The present invention relates to a liquid crystal composition for use in a flat panel display, a projection display, a printer, etc., a liquid crystal device and a method for driving the device, and a liquid crystal apparatus.
As a display (apparatus) most extensively used heretofore, CRTs (cathode ray tubes) have been known and have been widely used as monitors for displaying motion pictures for television sets and VTRs (video tape recorders) and as monitors for personal computers. However, because of its operation principle, a CRT is accompanied with various difficulties for static picture display, such as flickering, a low picture recognizability due to scanning fringes caused by insufficient resolution, and deterioration of the fluorescent screen due to sticking or burning. Further, it has been recently found that electromagnetic wave generated from CRTs can adversely affect the human body and health of VDT operators. Moreover, a CRT necessarily requires a structure including a large volume behind the screen and is inconvenient from the viewpoints of effective utilization of data processing apparatus and space economization in offices and at home. A liquid crystal display device is known to solve these difficulties of CRTs. For example, there has been known a type of liquid crystal device using a twisted nematic (TN)-type liquid crystal disclosed by M. Schadt and W. Helfrich, Applied Physics Letters, Vol. 18, No. 4 (Feb. 15, 1971), pp. 127-128. In recent years, a device using this type of liquid crystal and driven by TFTs (thin film transistors) as active devices or elements has been extensively developed and commercialized. This type of device (TFT-type liquid crystal device) uses a transistor for each pixel, is free from crosstalk problem and is being produced at a fairly good productivity for display sizes of 10-12 inches owing to rapid progress in semiconductor production technology. However, in order to provide a frame frequency of at least 60 Hz in view of a larger display size or motion picture display with no problem, the TFT-type device still leaves some difficulties, such as productivity, response speed of a liquid crystal material and a viewing angle.
On the other hand, a liquid crystal device of the type utilizing spontaneous polarization of liquid crystal molecules as a switching torque and having a high-speed switching characteristic and a memory characteristic has been proposed by Clark and Lagerwall (U.S. Pat. No. 4,367,924; Japanese Laid-Open Patent Application (JP-A) 56-107216). The liquid crystal used is a ferroelectric liquid crystal (FLC) generally in chiral smectic C phase or chiral smectic H phase. The ferroelectric liquid crystal (FLC) has a very quick response speed because of inversion switching based on its spontaneous polarization and also an excellent viewing angle characteristic, so that it is believed to suitably provide a simple matrix-type display device or light valve of a high speed, a high resolution and a large area. Further, a chiral smectic anti-ferroelectric liquid crystal device has been proposed recently by Chandani, Takezoe, et al. (Japanese Journal of Applied Physics. Vol. 27 (1988), L729-). In this regard, it has been quite recently discovered that a specific anti-ferroelectric liquid crystal material provides a V (character)-shaped response characteristic (voltage-transmittance (V-T) characteristic), free from a threshold and with little hysteresis property, advantageous to gradational display (Japanese Journal of Applied Physics, vol. 36 (1997), P.3586-). Further, as a liquid crystal material utilizing spontaneous polarization as a switching torque and providing a V-shaped response (switching) characteristic, several liquid crystals including surface-monostabilized FLC (e.g., Journal of Applied Physics, vol. 61 (1987), p.2400-), deformed helix FLC (e.g., Ferroelectronics, vol. 85 (1988), p. 173-), twisted-smectic FLC (e.g., Applied Physics Letter, vol. 60 (1992), p. 280-), threshold-less anti-ferroelectric liquid crystal, and polymer-dispersed stabilized FLC (e.g., SID ""96 Digest (1996), p. 699-) have been known.
Active matrix-type liquid crystal devices using the above liquid crystal materials for realizing high-speed display have recently been extensively proposed (e.g., as described in JP-A 9-50049).
Such active matrix-type liquid crystal devices using a chiral smectic liquid crystal having (anti-)ferroelectricity has still left problems in terms of afterimage due to hysteresis phenomenon, deterioration in alignment characteristic with time and a reliability such as burning phenomenon. Accordingly, it is strongly desired to solve such problems.
A principal object of the present invention is to provide a liquid crystal material and a liquid crystal device having solved the above-mentioned problems.
A specific object of the present invention is to provide a liquid crystal composition and a liquid crystal device which provide a high-speed responsiveness, a high image quality and a high reliability.
According to the present invention, there is provided an active matrix-type liquid crystal device, comprising:
a pair of substrates,
a chiral smectic liquid crystal disposed between the pair of substrates so as to form a plurality of pixels, and
a plurality of active elements provided to the pixels, respectively, for driving the liquid crystal device in a matrix driving scheme, wherein
the chiral smectic liquid crystal assumes two stable states between which a threshold voltage for switching from one of the two stable states to the other stable state is different from a threshold voltage for switching from the other stable state to said one of the two stable states and liquid crystal molecules change their alignment states so as to provide a halftone state depending on a voltage applied to the chiral smectic liquid crystal.
According to the present invention, there is also provided a method of driving the above liquid crystal device, comprising:
resetting the chiral smectic liquid crystal at an entire area of each pixel in a stabler state of the two stable states, and
applying a voltage depending on a display state to the chiral smectic liquid crystal at the pixel to effect writing for the display state.
According to the present invention, there is further provided a liquid crystal apparatus including the above-mentioned liquid crystal device, wherein a drive of the liquid crystal device is stopped after switching of the chiral smectic liquid crystal into the stabler state or interrupted in the stabler state of the chiral smectic liquid crystal.
The present invention provides a liquid crystal device, comprising: a pair of substrate each provided with an electrode, a liquid crystal disposed between the substrates so as to form a plurality of pixels, and a plurality of active elements provided to the pixels, respectively, for driving the liquid crystal device in a matrix driving scheme, wherein
the liquid crystal is a chiral smectic liquid crystal composition comprising at least two compounds including at least one species of fluorine-containing mesomorphic compound which has smectic phase or latent smectic phase and a structure including: (a) a chiral or achiral fluorochemical terminal portion capable of containing at least one catenary ether oxygen atom, (b1) a chiral or achiral hydrocarbon terminal portion, and (c) a central core connecting the fluorochemical terminal portion and the hydrocarbon terminal portion; the liquid crystal composition comprising at least 10 wt. % in total of at least one species of fluorine-containing mesomorphic compound having a fluorochemical terminal portion free from a catenary ether oxygen atom.
The present invention also provides a method of driving the above liquid crystal device, comprising:
alternately applying a reset signal of a polarity and a writing signal of a polarity opposite to the polarity of the reset signal to effect a gradational display depending on the writing signal.
The present invention further provides a liquid crystal composition comprising at least two species of fluorine-containing mesomorphic compounds each of which has smectic phase or latent smectic phase and a structure including: (a) a chiral or achiral fluorochemical terminal portion capable of containing at least one catenary ether oxygen atom, (b2) a non-racemic achiral hydrocarbon terminal portion, and (c) a central core connecting the fluorochemical terminal portion and the hydrocarbon terminal portion; said at least two species of fluorine-containing mesomorphic compounds including at least two species of chiral fluorine-containing mesomorphic compounds which have mutually different absolute configurations or mutually different signs of spontaneous polarizations and occupy at least 30 wt. % in total of the liquid crystal composition.
The present invention further provides a liquid crystal device, comprising: a pair of substrate each provided with an electrode, a liquid crystal disposed between the substrates so as to form a plurality of pixels, and a plurality of active elements provided to the pixels, respectively, for driving the liquid crystal device in a matrix driving scheme, wherein
the liquid crystal assumes at least two stable states and is the above-mentioned liquid crystal composition.
The present invention further provides a method of driving the above liquid crystal device, comprising:
alternately applying a reset signal of a polarity and a writing signal of a polarity opposite to the polarity of the reset signal to effect a gradational display depending on the writing signal.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.